The invention relates to methods of manufacturing heat treatable coated glass panes with a low-emissivity (low-e) and/or solar control coating. The invention also relates to coated glass panes produced by said methods.
Heat treated glass panes which are toughened to impart safety properties and/or are bent are required for a large number of areas of application, for example for architectural or motor vehicle glazings. It is known that for thermally toughening and/or bending glass panes it is necessary to process the glass panes by a heat treatment at temperatures near or above the softening point of the glass used and then either to toughen them by rapid cooling or to bend them with the aid of bending means. The relevant temperature range for standard float glass of the soda lime silica type is typically about 580-690° C., the glass panes being kept in this temperature range for several minutes before initiating the actual toughening and/or bending process.
“Heat treatment”, “heat treated” and “heat treatable” in the following description and in the claims refer to thermal bending and/or toughening processes such as mentioned before and to other thermal processes during which a coated glass pane reaches temperatures in the range of about 580-690° C. for a period of several minutes, e.g., for up to about 10 minutes. A coated glass pane is deemed to be heat treatable if it survives a heat treatment without significant damage, typical damages caused by heat treatments being high haze values, pinholes or spots.
It is worth noting that the parameter “haze” usually referred to when characterising the heat treatability of low-e and/or solar control coatings is often insufficient, as it does not fully reflect all types of defects that may arise during coating, heat treating, processing and/or handling of coated glass panes. Some of the known heat treatable coated glass panes show significant and clearly noticeable modifications of their optical properties and particularly of their reflection colour during a heat treatment. It is also appropriate to maintain the thermal properties of the pane during a heat treatment and this may be characterised in maintaining a similar sheet resistance or in some cases obtaining a lower level of sheet resistance.
Low-e and/or solar control coatings may be deposited by physical vapour deposition (PVD) processes, for example, sputtering. Sputtered low-e and solar control coating stacks are commonly made up of repeat sequences of substrate/base dielectric layer sequence/(Ag/dielectric layer sequence)n with each of the n dielectric layer sequences not necessarily having the same thicknesses or composition. Sputtered coating stacks are becoming more complicated in their nature due to the need for extra layers in toughenable coatings and the potential move to triple silver solar control stacks. Therefore it is now more common in the industry for n to equal 2 or 3. Since dielectric layers are generally thicker and slower to deposit than metal layers, stacks with a considerable number of such layers require a large number of cathodes in a production coating plant.
Previously, complicated coating stacks have required extensions to coating plants to get the sufficient number of cathodes to make the different materials in sufficient number and order. Extra pumping sections have to be included in the extension to allow the multiple reactive processes to run in sequence. This is done at great expense and with huge disruption, as the coating line needs to be stopped for an extended period for engineering installation. Each new cathode and pumping section also requires the accompanying power supply, vacuum pumps, conveyor sections, services, instrumentation and integration into the control system. It is also likely to cause restructuring of the downstream logistics and possibly even new civil works or building extension. As triple silver (n=3) and even quadruple silver (n=4) stacks become more common, these problems are likely to grow.
There have been attempts to alleviate these problems in the prior art. WO 2012052749A1 describes a process for producing a coated glass which involves depositing a chemical vapour deposited (CVD) coating on at least one surface of a glass substrate to produce a CVD coated glass, and sputter depositing a further coating on the surface of the CVD coated glass, wherein the further coating comprises at least three reflective metal layers. The CVD undercoating is preferably a layer of silicon oxide overcoated with a layer of titanium oxide. However the examples exhibit high levels of haze upon heat treatment and low levels of visible light transmittance both before and after heat treatment (see page 7, Table 3).
WO 00/32530A1 describes a process for the production of a heat-treatable low emissivity coated glass that comprises the steps of a) depositing an underlayer onto a glass substrate, and b) subsequently depositing a reflective metal layer by a vacuum deposition method, characterised in that the underlayer is deposited by a pyrolytic deposition process. The examples use a silicon oxycarbide underlayer and exhibit visible light transmittance values of from 73.2 to 76.3% before heat treatment (HT) and from 74.9 to 78.2% after HT. The emissivity values of the examples range from 0.060 to 0.076 before HT and from 0.065 to 0.072 after HT.
It would be desirable to provide a method for the manufacture of a coated glazing that alleviates the above-mentioned problems and results in a glazing that exhibits improved optical properties in comparison with prior art processes.